The next-generation turbo-diesel 6.6-liter Duramax engine, set to debut in the 2017 Chevrolet Silverado heavy-duty and GMC Sierra heavy-duty pickup trucks, will offer more torque, power and fewer emissions than ever before. GM debuted the engine at the 2016 State Fair of Texas.
Rated at 445 horsepower at 2,850 rpm and 910 pounds-feet of torque at 1,600 rpm, the new engine is essentially all new. GM engineers have touched just about every piece of the V-8 engine from tip to tail to make it stronger and more efficient. Yes, it is still the same displacement and it still offers a 32-valve setup, but other than that, every aspect of this new engine is new and upgraded.
The more powerful Duramax (with 19 percent more torque and 12 percent more hp) has a new, stronger cast-iron block able to house a larger-diameter crankshaft with stronger connecting rods and cast-aluminum pistons. The aluminum cylinder heads now incorporate intake and exhaust passages, is stiffer, and provides much better cooling.
Regarding the injection system, it uses smarter and more sophisticated high-pressure (capable of 29,000 pounds per square inch) fuel injectors that provide as many as seven separate fuel-delivery events per combustion event to make it quieter, more powerful and less likely to exhaust unburned fuel.
Possibly making the biggest impact to this Duramax is the new and larger, electronically controlled variable-vane turbocharger, which also provides greater performance for the exhaust brake system. On the emissions side, there are now three separate catalysts to reduce emissions, the first attached to the back end of the turbocharger; out-the-tailpipe emissions are reduced by 35 percent.
The new, higher-output engine will still be mated to the Allison 1000 transmission (originally born from the medium-duty truck segment), but it now has a stronger torque converter with several heavier-duty dampers, uses a stronger output yoke and provides faster lockup during heavy-load situations.
It's also worth noting how special the new intake hood design is to this powertrain. Because intake and exhaust temperatures are so important to diesel engines, GM designed its own hood/intake system, which allows the truck to get more and cooler air into the engine. The vented hood provides as much as 55 percent of the air going into the engine, yet is also able to separate and condense any water or dust particles that get sucked in, dumping its contents into the engine compartment before it ever gets close to the filter. As the air snakes through the hood, it cools. Then, along with the air intake mounted in the traditional spot (in the grille next to the passenger headlight), air passes through the heavy-duty filter before it's sucked into the diesel combustion chamber.
We had the chance to do some "light" towing with a few Silverado 3500 dually 4x4s while pulling a well-balanced 10,000-pound box trailer behind. We found the new powertrain a significant improvement from the previous generation in how responsive and powerful the new setup is off the line and when rolling from 40 to 70 mph. (We may or may not have spun a few dually tires during our drive.) The overall feel is stronger and more confident, but we still have a few gripes.
Unfortunately, even with modifications to the transmission, GM engineers still do not allow the driver to see what gear the transmission is in unless you pull it down into the manual setting. Also, the exhaust brake (still) only offers an on and off setting, and didn't seem to provide much impact with the trailer on hand (though we did notice some strong grade braking). Finally, although the diesel exhaust fluid tank is a little larger, providing longer filling distances, the tiny fill cap is still inside the engine compartment with an inconveniently small filler hole, almost guaranteeing a messy operation for customers.
The new diesel engine and transmission upgrades put the GM HD players (in terms of torque) just underneath the new 6.7-liter Ford Super Duty Power Stroke, which offers 440 hp and 925 pounds-feet of torque, and just above the 6.7-liter Ram Cummins, which offers 385 hp and 900 pounds-feet of torque. Like Ford, GM will have only one power rating for its engine combination regardless of model configuration.
The new powertrain will be available on 2017 Silverado and Sierra HDs in the first quarter of 2017, and pricing will be slightly more expensive than the current-generation diesel option. Although nothing official has been released yet, the new powertrain will likely cost around $9,000. More details to come.
Cars.com photos by Angela Conners; manufacturer images